The present invention relates to a percutaneous surgical instrument for the excision and removal of a wide range of tissues. More particularly, the invention resides in a rotary cutting instrument that is particularly well suited for operation at a broad range of rotational speeds, and which is capable of cutting tough tissue, such as may be encountered during orthopedic or spinal surgery. Although the present invention has application in many surgical procedures, the following disclosure will pertain principally to minimally invasive cutting instruments used in the field of spinal surgery.
In the field of spinal surgery, one problem that is frequently diagnosed and treated concerns degeneration or herniation of an intervertebral disk. Treatment of these diagnosed conditions often requires some degree of fusion between the adjacent vertebrae serviced by the affected intervertebral disk. In spinal fusion procedures of this type, it is typical to entirely remove the affected disk for replacement by bone graft material, or in some cases, by a prosthetic disk.
Within the last decade, techniques for percutaneous diskectomies have been developed in which the disk tissue is removed by a cutting instrument inserted percutaneously. These techniques have virtually eliminated the need for highly invasive surgical procedures to remove disk tissue. One such system is described in the patent to Onik, U.S. reissue Pat. No. 33,258, which shows a "tube within a tube" cutting instrument. The device disclosed in the Onik patent incorporates a rotary inner cutting sleeve operated within the central bore of an outer cutting sleeve.
Another instrument for percutaneous tissue removal is shown in the patent to Bonnell et al., No. 4,203,444. The Bonnell device is of the rotary genre in which an internal blade rotates within an outer cannula having a side facing shaving port. In the Bonnell device, along with other rotary cutters of this type, the axial edges of the shaving port coact with the axial extending edges of the internal blade in a scissors-type action to shear tissue. The internal blade is hollow to allow the tissue shavings to be aspirated through the instrument during the cutting operation. Rotary cutters of this type are often susceptible to becoming clogged as the excised tissue spools around the internal rotary blade, thereby clogging the aspiration channel or even stalling the rotation of the cutting blade.
Another problem common among both rotary and linearly reciprocating devices is an inability to cut very tough tissue using a percutaneous cutting device. Certainly, larger cutting instruments driven by larger motors are capable of cutting very tough or hard tissue. However, no prior device has been able to avoid the trade-off that is forced between a minimally invasive cutting instrument and the ability to cut a variety of tough tissues without clogging or stalling the cutting instrument.
Another disadvantage experienced particularly by the rotary devices is the need for an outer cannula having a shaving port that includes a sharp edge to assist in the cutting or shaving operation. This typically necessitates a rigid cutting instrument, such as the Bonnell device. This requirement in turn limits the environment in which a percutaneous cutter of this design can be utilized because the external tube or cannula is not flexible enough to be bent or guided around anatomic features, as may be required in many spinal surgical procedures.
There is therefore a need in the field of tissue excision and removal for a surgical cutter that is well suited for minimally invasive uses, yet that is still capable of cutting the tough tissues encountered in spinal and orthopedic procedures. The cutting instrument must be capable of excising the tissue cleanly without tearing, and of aspirating the tissue pieces efficiently and without clogging. The instrument should further be flexible to allow both the outer tube and the inner tube to bend as required to reach the cutting site. These and other needs are addressed by the present invention.